Touch panels mounted on the display panels of the LCDs have become more and more commonplace as their prices has dropped over the past years. The touch panel itself serves as input and output devices and is generally mounted on a personal digital assistant (PDA) or a handheld computers in order to replace the function of a keyboard, thereby minimizing a storage space. The PDA is often used by a consumer to conduct daily performances, such as taking memos, for storing addresses and phone numbers, taking notes and keeping track of daily business appointments and etc.
Referring to FIG. 1, a typical touch panel 10 of resistance system is shown, is adapted to be mounted on a display panel of a portable PDA because the latter has simple circuit structure and does not require special input device, and includes a indium tin oxide (ITO) layer 12, an ITO film 16, and a plurality of spacers 14 disposed between so as to insulate one from the other. The ITO layer 12 is generally mounted on the display panel while the ITO film 16 is disposed above the ITO layer 12 via the spacers 14. The opposite sides 12a, 12b of the ITO layer 12 have different voltage levels, a voltage gradient is resulted in the ITO layer 12 and extends in the Y direction. In the similar manner, another voltage gradient is resulted in the ITO film 16, and extends along X direction perpendicular to the Y direction by virtue of different voltage levels at two opposite sides 16a, 16b thereof. When a user touches the ITO film 16, the two contact each other and the change in the electrical field is noted and the coordinates of the point of contact are calculated. Once the coordinates are known, a special driver translates the signal at four corners of the ITO film 16 so as to identify the point of contact. Note that the touch panel 10 of the resistance system can only detect a single point of contact, and is unable to detect a finger print pattern having several ridges and valleys forming several points of contact.
FIG. 2A shows a top planar view of a conventional touch panel 20 provided with a fingerprint recognizing technology. FIG. 2B shows a cross-sectional view of the conventional touch panel 20 taken along lines a-a in FIG. 2A, and is mounted on the display panel 30 of an LCD system. The conventional touch panel 20 includes a TFT array, a plurality of data lines 24, a plurality of scanning lines 26, a transparent conductive pattern layer 27, a transparent flexible conductive film 28, and a spacing pattern layer 29. The data and scanning lines 24, 26 criss-cross one another to form a plurality of square configurations, each between adjacent pairs of the lines 24,26. The thin film transistor (TFT) array includes a plurality of thin film transistors 22, each is disposed within a respective square configuration, and has a drain D, a gate G respectively connected to a respective data line 24 and a respective scanning line 26, and a source S. The transparent conductive pattern layer 27 is disposed above the data and scanning lines 24,26, and includes a plurality of conductive islets 27a, each of which fills a respective square configuration and is connected to the source of a respective thin film transistor 22. The flexible conductive film 28 is disposed above the transparent conductive pattern layer 27. The spacing pattern layer 20 is disposed on the display panel 30, disposed on the touch panel 20 surrounding in such a manner to support the flexible conductive film 28 thereabove so as to space the flexible conductive film 28 apart from the transparent conductive pattern layer 27. When a user's finger touches the flexible conductive film 28, a signal is transmitted to the sources S of the TFTs 22 via the conductive islet 27a, where the scanning lines 26 scan the data lines 24 consecutively via the TFTs 22 so as to identify the coordinates of the points of contact.
The light provided by the backlight module in the LCD system reaches the aforesaid conventional touch panel only after passing through the display panel 30, transparent conductive pattern layer 27 and flexible conductive film 28 to show the image. Though the transparent conductive pattern layer 27 is made from ITO or indium zinc oxide (IZO) for providing highly-transparent ratio, during the traveling of light through the touch panel 20, a portion of the light is absorbed by the transparent conductive pattern layer 27 and will affect the luminance efficiency of the display panel 30. In case the touch panel 20 covers partially of the display panel 30 so as to provide fingerprint-recognizing ability, the portion of the display panel 30 covered by the touch panel 20 is poorly illuminated when compared to the remaining portion of the display panel 30. Accordingly, how to improve the transparent conductive pattern layer 27 of transparent ratio for the display quality of display panel 30 has a very important effect.